RFR (S): 8029888: PPC64: (part 219): smaller changes needed to build c2

[Lindenmaier, Goetz]

Hi,

Recent changes make two other smaller shared adaptions necessary
for the ppc port:
http://cr.openjdk.java.net/~goetz/webrevs/8029888-0-basic2/

First, introduce replacement variable $$CondRegister in adl.

Further, the latest changes to compressed klasses broke an
optimization on ppc.  This change contains a better way
to check for the max size of a compressed klass.  I need not mask
sign extension bits if compressed klasses are at most 31 bits.

Please review and test this change.

Best regards,
  Goetz.